Comissioning of Chp Systems.Pdf
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National Conference on Building Commissioning Whitepaper on: Commissioning of Combined Heat and Power Systems Information was compiled with support fr o m the U. S. Department of Energy and Oak Ridge National Laboratory Newport Beach, California April 22 – 24, 2008 EXERGY Partners Corp. 12020 Meadowville CT Herndon, VA 20170 (703) 707.0293 phone (703) 707.9566 fax www.exergypartners.com ABSTRACT This paper explores recent commissioning practices of Combined Heat and Power (CHP) systems applied within the built environment. CHP systems are more complex involving increased attention to atmospheric emissions and electric grid interconnection and sophisticated control logic. This study focuses on four specific buildings: a San Francisco hotel retrofitted with a “packaged” microturbine generator/double-effect chiller plant; a Los Angeles casino retrofitted with an advanced reciprocating engine, hot water heat recovery and a single-effect absorption chiller; a Brooklyn laundry retrofitted with two reciprocating engine generators and a hot water heat recovery system; and finally a state-of-the-art hospital in Austin, TX with a combustion turbine, heat recovery steam generator, absorption and electric chillers and thermal storage. These case studies provide design insight, identify commissioning issues and lessons learned from the initial operation. The author’s takeaway from this brief study is that there is a need to establish a set of commissioning best practices for CHP systems. INTRODUCTION Commissioning CHP systems in commercial and institutional buildings requires broad experience covering small power plant systems (less than 25 MW), heat recovery, thermally activated technologies, electric switchgear, grid interconnection operation and safety, sound and vibration, emissions control as well as building, mechanical and electrical systems integration. While CHP systems are common throughout industrial sites accounting for about 84 GW of electric capacity in America, less than 1 GW of power is currently operating in the built environment. The use of CHP systems in buildings is likely to increase as the need to reduce carbon emissions grows and public policy moves to monetize carbon emissions. What is really different about CHP systems? Let’s break it down first by major components and then examine the integrated system. 1. Continuous duty drivers – The current span of CHP power systems consist of reciprocating engines generally under 10 MW, microturbines between 65 and 250 kW and combustion turbines between 1 and 15 MW. Fuel cells are also in use between 5 kW and 1.5 MW, but are generally quite expensive at this time. 2. Emissions – Onsite combustion requires a firm understanding of the federal, state and local air permit requirements. It is important to know that air permits are indeed essential before any construction is commenced. Generally speaking all these power technologies are capable of being sited anywhere in the USA, with perhaps a few counties in California currently limiting the use of current state-of-the-art reciprocating engines even with after-treatment. The principle question for emissions is generally a matter of cost and not feasibility. 3. Generators – There are two principle classes of generators: induction and synchronous. Induction generators produce electrical power when their shaft is rotated faster than the synchronous frequency of the equivalent induction motor. Induction generators are not self- exciting, meaning they require an external supply to produce a rotating magnetic flux. The external supply can be supplied from the electrical grid or from the generator itself, once it starts producing power. A synchronous generator is a machine that generates an alternating voltage when its armature or field is rotated by an engine, or other means. The output frequency is exactly proportional to the speed at which the generator is driven. The functional purpose and interconnection issues will determine the generator design. 4. Interconnection – Grid interconnection requirements have certain common characteristics with respect to operations and safety, like compliance with IEEE Standard 1547, however, state and local utility requirements and grid characteristics (radial or network) will vary dramatically. This is an area where minimum commissioning is usually dictated by the utility and site commissioning issues are sometimes missed. 2 of 27 5. Waste heat recovery schemes – This covers the wide variety of means to recover waste heat from generators and/or processes for delivery to thermally activated technologies. The range of systems covers ducting and reclaiming heat from hot air sources (process, engine, turbine, microturbine exhausts) and recovering heat in the form of hot liquids (engine jacket water, oil cooling and exhaust, process streams, etc.). 6. Thermal technologies – The most common technologies are heat recovery heat exchangers, heat recovery steam generators, absorption chillers, desiccant dehumidifiers and organic Rankine cycle (ORC) generators. Turning waste heat into hot water or steam is generally the simplest and most cost effective. Absorption chillers can convert the waste heat to chilled water but add another level of complexity and cost to the project. Absorbers are either provided as low-temperature single or high-temperature two stage machines. Desiccant dehumidifiers can be coupled to hot air streams in the 250F range or hot water in the 190 F range. ORC can absorb 400 – 600 F heat and provide electricity at 10 to 15% cycle efficiency. 7. CHP integration – CHP integration focuses on successfully integrating the power generation with the thermal heat recovery and thermally activated technologies. The effectiveness of this effort varies widely depending on the degree of pre-engineering and packaging. Retrofit systems require more flexibility and ability to balance the system in the field. 8. Building system integration – Integrating a CHP system to building loads and systems is critical and requires knowledge of the buildings operation (retrofits) or design intent (new building). Here too, flexibility and ability to balance systems is also essential. There are clearly more elements that need to be considered in applying and commissioning today’s CHP in buildings. Understanding the components, their integration requirements and having the flexibility and means to balance systems is essential. Finally having a commissioning plan that tests the system’s capabilities is essential. COMMISSIONING A MICROTURBINE/CHILLER CHP PLANT AT A SAN FRANCISCO HOTEL The CHP System was installed at a deluxe 336 room hotel in downtown San Francisco. The hotel is owned by a real estate investment trust whose portfolio includes over 100 properties in 26 states including large holdings in California, Florida, Georgia, Boston, New York, and Washington DC. CHP System Design The CHP system is a predesigned standard product that contains four microturbines each rated at 60 kW of electrical power at a 59ºF (15ºC) sea level condition. Rated NOx emissions are less than 9 ppm at 15% exhaust oxygen, which met local emission requirements in force at the time of the installation. The exhaust from each microturbine is manifolded together to deliver input energy to a double-effect absorption chiller (Figure 1). The lithium bromide/water chiller consists of an evaporator, absorber, condenser, high temperature and low-temperature generators, solution heat exchangers, refrigerant and solution pumps, purge, controls and auxiliaries. The chiller is an adaptation of a direct-fired chiller that increases the heat transfer area of the first stage generator to compensate for the lower temperature inlet energy (microturbine exhaust gas). Because it is a double-effect device, the chiller effectively converts the input thermal energy to chilled water and achieves a coefficient of performance (COP) of approximately 1.3. The double- effect feature also permits a manual change-over of the chiller to operate as either a chiller or heater. Thus, the CHP system can provide either space chilling or space heating. The control system includes a diverter valve in the duct between the microturbines and the chiller. If the chilling demand is zero, this valve diverts the microturbine exhaust to atmosphere. If a chilling 3 of 27 demand exists, the diverter is positioned to deliver the energy required for the chiller to meet the demand. The ability to isolate the chiller under no load situations is important to avoid excessive concentrations within the chiller and possible solution crystallization. Also shown in the figure are the fuel gas boosters (FGB) that elevate the pressure of the natural gas fuel supplied by the gas utility to the level required by the microturbine. Each CHP System uses one FGB for a pair of microturbines. The FGB is powered by the DC power produced within one of the microturbine pair and therefore that microturbine experiences a parasitic electrical load that diminishes its AC output. DIVERTER FUEL GAS BOOSTER VALVE COMPRESSOR DOUBLE-EFFECT ABSORPTION CHILLER 60 KW MICROTURBINE Figure 1 CHP System Schematic Figure 2 Before and After CHP System Retrofit Figure 2 shows before (left) and after (right) the CHP system retrofit. It should be noted that the lower right garden serves as a highly coveted entertainment spot for this Mobil five diamond property. The site configuration required modification from the standard design field assembly. 4 of 27 Table 1 details the performance specifications of the CHP system at 95ºF